1. Field of the Invention
The invention generally relates to a backlight module.
2. Description of Related Art
In recent years, as electronic products become common, the display panel that provides the display function for the electronic products has come into focus among designers. There are various types of display panels that can be selected for use according to the designs of the electronic products. Some of them are not provided with a light-emitting function, and thus a backlight module needs to be disposed under the display panel to serve as a light source, so as to achieve the display function.
Such a backlight module usually includes an assembly frame, a light source, and a light guide plate. According to a relationship between the light source and the light guide plate, backlight modules may be categorized into two types, which are direct type backlight module and edge type backlight module. Take the direct type backlight module as an example, the light source and the light guide plate are installed in the assembly frame, wherein the light source is located under the light guide plate, such that the light emitted by the light source is guided by the light guide plate to be emitted out of the backlight module. In addition, the backlight module may use a variety of types of optical films as required, such as a prism film, a diffusion film, a brightness enhancement film (BEF), a polarizer film, and other suitable optical films. The optical film is disposed on two opposite sides of the light guide plate for adjusting a transmission path or distribution of the light emitted by the light source.
In order to eliminate the mura phenomenon, i.e. non-uniform brightness distribution, of the display device that uses the backlight module, the backlight module may use a perforated reflective film having high reflectivity to adjust the transmission path and distribution of the light emitted by the light source. The perforated reflective film has a plurality of perforations, and the number or area of the perforations differs between different regions so as to differentiate the light transmission amounts in these regions. For example, fewer or smaller perforations are formed in a region of the perforated reflective film corresponding to the top of the light source, so as to reduce the light transmission amount. In contrast thereto, more or larger perforations are formed in another region of the perforated reflective film not corresponding to the light source so as to increase the light transmission amount. Accordingly, the light emitted by the light source first passes through the perforated reflective film for adjusting the distribution profile before being transmitted outward, by which the uniformity of the light is improved.
In addition, for the backlight module to achieve wide color gamut (WCG), the backlight module may use blue light emitting diodes (LED) accompanied with a quantum dot enhancement film (QDEF). The quantum dot enhancement film converts part of the light emitted by the light source into a light having a different wavelength. For example, partial blue light is converted into a yellow light, and then the two lights having different wavelengths are mixed to produce a white light. Due to the perforated reflective film disposed in the backlight module, there is more light reflection between the quantum dot enhancement film and the region with fewer perforations of the perforated reflective film (i.e. the region corresponding to the top of the light source). As a result, in the region above the light source, more light is converted into the yellow light, which causes the overall light-emitting color of the backlight module to be non-uniform, and this phenomenon is called color shift.